Production of furfural and acetic acid from pentosan containing material



Sept. 14, 1954 G* NATTA 2,689,250

PRODUCTION OF FURFURAL AND ACETIC ACID FROM PENTOSAN CONTAINING MATERIAL Filed April 26. 1951 63 'u Ifo A/ if j -zhuentoyg f hum, /QtorhQ/Lts,

Patented Sept. 14, 1954 RODCTUN .i OF FURFURAL.. AND... ACETIG. ACID'FR'OM `PENTOSAN CONTINING MA- I TERIAL Giulib Natta; l. Mil-arr,"I Italy, Vassigner'.-to-.lOronzio' Dei-Noraflmpianti;:Elettrochimici; Milan,--.Italy,^.

`a corporation-of-Italy Application Apr112`6; 1951, SeriaiINd: 22.32062(1 4 Claims.:

It 'i-s krioWri1 tofprodiic'e frfural aridil acetic 'facid i fromv pentosanicontai-iiiiigmateriallsucha asA oai-fv hulls;` shellslof f sunflower" :seedssiri'cer hulls-@corneL cobs and the-like; hy liieating-faidampened mass ofr said niaterialfadinifxed Witha: furfuraii.forniing acid catalyst, such as suilphiiricfy acid,byf meansof alcdrrent of steam; `:whereby the .volatile reaction'pr'oducts, includingfurfuraig.are carriedi along-@Withthe i current. otisteam issuingirom. theireaction vessel.

It i is an object ofthe-presenti invention lto' ;pr.o videa processnwnerein' the' :consumption .oiioata-i lyst :greatly` reduced;` the'freactonr taking :piace-i inV the 1 presence'A 'of the .catalyst :im ai concentra@` tion which is substantially greater than the conf-1 centrati'onof.l thefc'atalyst'as' itfis introdiicedfinto themassl-rofr the istartingfmaterialg andcthefmajorf part l of." the f catalystl beingreccvered: and; rez: cycledif L Another ."ob'iectf of my; inventionizisato :provide4 ai processi: in Wh-c'hkthei vegetab1'e11materia1.; en;I haustedl isdischargedffrom the reaction: tvesselr: free fromany content/fof the'fa'cid catalystand free Yfrom moisture; wherebyit' cani `loefstilfl uti i li2e'd;.lfor instance, z asia: lfl'ielg" with.f no: dangers-v to: the furnace infgwhicl-rtit iszsournt;y forsprcdricing 1: the steam'. 'required for? `'carrying f outf the process? itself."` f' A frthertob'ject loirthe.V present'invention visto; provide azayield oftifiirfurals: which. isY higher thank that 1i obtained; `with the sknownr processes;4 and' which is close to its theoretical value.

According 'to .my invention; Il fedicontiriuously the; pentosanfcontaining rmiifteriai inf afcoiumm together Wit-,tiran :amount "offwaterr and1 Il intros-:- dlicet'also" continuouslyi, a'. cormra;rativeiyrV small'. quantity of? hydrochloric:A acid:therein;` atv the bottom'o'i thebcolumrirI introduce fawiiow "oftsuper lheated?steam and :IfWithdrawftliet` gaseous prod; ucts from nearthe` top"=oiftliecolum1r:. Them-pe Wardowfofsteanr-:tnrough "the columns: cansesfy thefacid .tofevapo'rate Ifrloml'thebottomtlayersfof' the-` 'mixti-ireV4 so'. `that the?. colderrsuperior .layers receive this acid; which; isf. pamtiailrf'condensed` and addedftothe' aciifalreadyl existingftlfierein..

Inrthatizorie `ofthe coiunirntiierefore; a cori'-l centration. of the hydrochloric acid.l takespiace by rectification lof the' acids'o-l-ut'iori' descending together with: thev vegetabie material and fthe acid vapors flowing up? inside the 4cohirnr'illthere"` tiir'ough?.

theI intermediate zone of' the columnxthe reaction takes place'inthe lpresence i of thel concentrated acid Solution; WhileV theexhausted` ma teriai" at"th"every"bottm of the" column` is dissl (Cl. 2GB-*347.9%

2: charged? i free 1 from:I acid.: asywelli. asf: free from; moisture:-

The. present' application'.l isza continuation:1inil parti of .ther applications aser.: NflV 720,476,1led11; January-6, 1947, nowlrabandonedsand Ser.;`

whichlwmzbeibetrzunderstoodrfromthe'ionowingzdescriptionfin connectionl therewith;

Inth "drawings:

Fig: i 1 isa'f diagrammatic sectional: view'of one# apparatus;v

Fig: 2 .is ai simi-ian viewv ofianotheryapparatusl@ With:reference toi.: Figli 1, the 'apparatus com. sistsiof, a column.l I; .into .WhichiaxconduitiZ-penee trates at tire"v topp .thei-conduit1.21:.comm1inicatesz with .an endlessfscrewfconveyorf fed byffa 'hopeperil:

The1..coiumrr.l .riscmadeiof acid-resisting :matesV rial;4 or v'else'toifcoppeieor :other :irretalg-y provided@` thatV thef'mantlewisr.steamfjacketed oriA otherwise; heated', so asl to" prevent; condensation; ofxthe" acidavaporsor: lits inner surface;

Thefbottomiendzofthe column l communicates; withasecond conveyor 5 discharging into an; out-r let hopper 6 provided With:c1osing'f nieansffl.` Ai frustowconicaid'efiectoir providedxjust ab'ove the:conveyor:.fandf` a pipe; s'eriters: the: col'umm behind said defiector; anotiiernpipef lil .is1fcoi'r-r nectedi to .the -i' col-umn inzcorrespondence"to" the tcp :portion:behindithefendfot thefconduit 2.1:

Avmixture consisting ofgcommmutedvegetable material; containing pentosamu sucinV as. corna: cobsfor ricevl'rulls', 15 percentlwater and '3.:lper cenit hydrochloric acid; introduced i-nto; the hoppervd-,ivv'herefrom the conveyor 3f feeds it-.intor theucolumnx! ;1 260 loer centbynveight'of steamy superheatedf ati 360 C.- is'-introducedvinto-1the` columna! :throughathepipef9.1 The steanrcausesv ioothftheV Water: and riryd-rochlol'ic-J acidy in.- the zone. immediately abovethe deflector.' 81110 disftii towardsf thet superior ."layersgf. Wl'iicl'i` i getfV enrichedntherefdre, .Withfzacidf content; the-:latten may beffen-instance; asf; highasf 6:12 `per cent by i Weight With` :respect to the -fvegetabie t materia'i in tn'ezone indicatedbyd t-in'sthedrawingz; In' this zone; .thereacticn takes 'place and. `furfurai isi.` formed.- from" the` pentosans: containedfin- 'the' vegetabiefzmaterial. f

Fromriitheitpipe i 6 a1 gaseous :iicW issues 1 con-1 sisting of lz'inper'cent steam;y 215i per: cent Iiydro'oiiiric s acid and feitiier 13L156f'per` centorf 7`-`9"v per` cent furfu'ralf according *to* Whetherv corn"-v celos` or v*rice^"1i"ul1`- has *been employedl as rstart-ing 3 material, said iigures being taken with respect to the weight of the vegetable material which is being passed continuously through the column I. A small portion of the hydrochloric acid, that is about 0.5 per cent, is combined with the exhaust material in the form of chlorides.

The remaining major part of hydrochloric acid issuing through the pipe I is recovered by any suitable means, so as to be partially employed again in the cycle.

The furfural and the acetic acid are separated from the condensed water and collected also according to the known art.

The exhausted material is discharged by the conveyor 5 through the bottom hopper 6 either continuously or at short intervals, at such a rate that the material takes a time of 3 to 8 hours for passing through the column from top to bottom; the material discharged from 6 is practically free from hydrochloric acid and is practically dried, due to the high temperature of the superheated steam introduced into the column I through the pipe 8 and can be utilized for producing the steam in any suitable boiler; the production of steam, therefore, involves no expense in this process and consequently the cost of the furfural and acetic acid produced is exceedingly low, in comparison to the known methods of producing them.

According to the manner of carrying out my invention represented in Fig. 2, the apparatus is quite similar to that shown in Fig. 1, but is provided with a further inner delector I2 and a further pipe I3 in correspondence thereto.

From the top of the apparatus only the vegetable material admixed with, say 15 per cent Water is introduced, while a flow of 2 to 3 per cent by weight of gaseous hydrochloric acid is introduced into the column through the pipe I3.

Owing to the introduction of steaim through the pipe 9, a zone of maximum concentration of acid with respect to the material forms at I I due to the same reasons set forth in connection to Fig. 1 and the furfural produced (yield 8 to 16 per cent by weight relative to the starting material according to the nature of the latter) flows out together with the steam and the hydrochloric acid through the pipe I0.

Also in this case the exhausted vegetable material is dry and free from acids and the process proceeds continuously.

The amounts of water, hydrochloric acid and steam as well as the temperatures mentioned in the above example may undergo considerable variation according to how the reaction is conducted; the total amount, with respect to the vegetable material, of the water including the moisture contained in the material itself, can vary within a range of 15 to 30 per cent; the tot-al hydrochloric acid introduced must be at least 1.5 per cent for a suiciently active reaction and can be as high as 6 per cent, but in general an amount of 2 to 3.5 per cent is considered to be satisfactory.

The hydrochloric acid may be introduced either as wholly contained in the acid solution admixed with the starting material, or wholly in the gaseous form through the pipe I3, or else partially as a solution from the top of the column and partially from the bottom in the gaseous form through the pipe I3. The amount and temperature of the superheated steam largely depends upon the quantity of water introduced in the column and the moisture contained in the starting material; the greater is the quantity of the steam, the lower can be its temperature, so that the total heat introduced in the column be 4 suiiicient to evaporate all of the water contained in the mixture and to carry out the hydrochloric acid and the furfural in the gaseous form.

In general, the quantity of steam may be comprised between and 400 per cent and its temperature maycorrespondingly vary between 350 and 200 C.

The amount of hydrochloric acid and steam. however, can be still reduced, according to another manner of carrying out my invention, if gaseous chlorine is admixed with the steam introduced in the column through the pipe 9, or anyhow introduced into the column near the bottom thereof, about the same level where the steam is introduced.

For instance, a quantity of chlorine corresponding to 2-3 per cent relative to the weight of the Vegetable material is admixed with a quantity corresponding to 200 per cent of steam superheated to 280 C. and these two gaseous iiuids are introduced through the pipe 9 into the column I which is charged with the vegetable material, for instance rice hulls, soaked with a 10 per cent solution of hydrochloric acid; the quantity of this solution may be 10 per cent by weight of the vegetable material.

I am aware that the use of gaseous chlorine as a catalyst for producing furfural from pentosan containing material has already been proposed in the Patent 2,488,981.

Such process requires a comparatively low consumption of steam in comparison with other known processes, but with certain materials, such as for instance rice hulls, the yield is relatively poor.

According to the last mentioned manner of carrying out my invention, however, the yield is much greater. Moreover, under the action of the hydrochloric acid solution, the pentosans undergo a preliminary hydrolysis to pentoses and the successive hydrolysis to furfural is enhanced in the middle zone of the column where the concentration of hydrochloric acid is increased due to the action of the chlorine and the effect of rectification caused by the acid material descending through the column; should the hydrochloric acid solution not be present in admixture with the starting material, the pentosans do not undergo a preliminary hydrolysis and the yields are lower due to the oxidizing action of the chlorine which is still present in the bottom zone of the column.

On the other hand the addition of chlorine to the steam reduces the consumption of the latter for a given superheating temperature, because the reaction with chlorine is highly exothermic.

The vapors issuing from the pipe I0 are practically free from chlorine; they can be first partially condensed so as to obtain a solution of hydrochloric acid which can be utilized for impregnating the starting material in the continuous process. By completing the condensation of said vapors an acid solution containing acetic acid, hydrochloric acid and furfural is obtained, in which the furfural content is about 4-5 per cent, corresponding to the yield of about 8 9 per cent relative to the weight of the vegetable material treated, if the latter is rice hulls. If corncobs are treated, the above ilgures are 5-7 per cent and 13-15 per cent respectively.

If the starting rice hulls are impregnated with l5 per cent of the aforementioned solution of hydrochloric acid (10 per cent of acid relative to the water) and 250 per cent of steam at 280 C. together with 2 per cent chlorine are intro- 5 duced through the pipe 9, the yield of furfural is about 9-10 per cent relative to the Weight of the rice hulls treated.

If corncobs are treated in the same last mentioned condition the yield of furiural is about 14-16 per cent relative to the weight of the dry corncobs introduced.

Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be performed, I declare that what I claim is:

1. A process for producing furfural and acetic acid from pentosan containing material, which comprises continuously feeding unheated pentosan containing material together with water into the top of a column having a top, a bottom and an intermediate zone, whereby they descend through said column to the bottom thereof, introducing hydrochloric acid into said column at a point above the bottom thereof, vaporizing the water and hydrochloric acid contained in said material at the bottom of the column by means of superheated steam introduced into the column at the bottom thereof, thereby producing in the liquid phase of the material descending through the column at a point above that at which vaporization of the water and hydrochloric acid takes place a rectifying effect by the passage of the acid vapors through said descending material, said rectifying effect being due to the partial condensation of the hydrochloric acid vapors by the water contained in the cold material entering at the top of the column and to the fact that the descending material always has a lower temperature than the ascending vapors, whereby the acid concentration in the liquid phase increases relative to its concentration at the point of introduction of said acid and reaches a maximum at a point intermediate the top and bottom of the column, said point of maximum concentration constituting a zone of maximum hydrolysis of said pentosan containing material, Withdrawing the resultant gaseous products containing furfural and acetic acid from the top of said column, and continuously discharging the exhousted material, dried and free from acid, from the bottom of said column.

2. The method of producing furfural in a single continuous process which comprises introducing furfural yielding plant material containing water, and hydrochloric acid as a catalyst, into the top` of a distillation'column, introducing super-heated steam in the bottom of said column, and regulating the iiow of the furfural yielding material and catalyst and the volume and temperature of the steam so as to maintain a low catalyst concentration in the top of the column to promote conversion of the pentosan content of the furfural yielding material to pentose and so as to vaporize and recondense a portion of the catalyst in the mid-portion of the column to cause an increase in catalyst concentration to promote conversion of the pentose to furiural, discharging the furfural, steam and vaporiZed products adjacent the top of the column below the inlet for the furfural containing material, and discharging the dry spent plant material substantially free from catalyst and water from the bottom of the column and below the steam inlet thereto.

3. The method o producing furfural which comprises continuously introducing moist furiural yielding plant material and an aqueous solution of hydrochloric acid into the top of a distilling column, introducing a hydrochloric acid producing catalyst into said column above the bottom thereof, continuously introducing superheated steam into the bottom of said column at a temperature and in sumcient volume to remove the furfural and other volatile reaction products from the top of said column, continuously contacting the steam moving upwardly in said column with descending moist furfural yielding piant material containing hydrochloric acid to condense a portion of said steam and increase the catalyst concentration in the condensation zone, continuously removing the uncondensed steam, furiural, vaporized catalyst and other volatilized reaction products from the top of said column, and continuously removing the spent iurfural yielding plant material from the bottom of the column below the steam inlet.

4. The method of producing furiural which comprises introducing unheated moist iuriural yielding plant material into the top of a distilling column having a top, bottom and intermediate section, introducing a hydrogen chloride containing catalyst into said furfural yielding plant material in said distilling column, continuously introducing super-heated steam into the bottom of said column at a temperature and in suiiicient volume to distil the furfural, water and other volatile reaction products from said furfural yielding plant material, passing the volatilized products into contact with the colder upper layers of said iuriural yielding plant material to condense and return a portion of said catalyst and other volatilized material into the mid-portion of the column, continuously removing uncondensed steam, furfural, vaporized catalyst and other voiatilized reaction products from the top of said column, and continuously removing the spent furfural yielding plant material from the bottom of said column below the steam inlet.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,322,054 Ricard NOV. 18, 1919 2,140,572 Brownlee Dec. 20, 1938 2,382,390 Millar Nov. 7, 1944 2,369,655 Boehm Feb. 20, 1945 2,488,981 Marchiaro Nov. 22, 1949 

1. A PROCESS FOR PRODUCING FURFURAL AND ACETIC ACID FROM PENTOSAN CONTAINING MATERIAL, WHICH COMPRISES CONTINUOUSLY FEEDING UNHEATED PENTOSAN CONTAINING MATERIAL TOGETHER WITH WATER INTO THE TOP OF A COLUMN HAVING A TOP, A BOTTOM AND AN INTERMEDIATE ZONE, WHEREBY THEY DESCEND THROUGH SAID COLUMN TO THE BOTTOM THEREOF, INTRODUCING HYDROCHLORIC ACID INTO SAID COLUMN AT A POINT ABOVE THE BOTTOM THEREOF, VAPORIZING THE WATER AND HYDROCHLORIC ACID CONTAINED IN SAID MATERIAL AT THE BOTTOM OF THE COLUMN BY MEANS OF SUPERHEATED STEAM INTRODUCED INTO THE COLUMN AT THE BOTTOM THEREOF, THEREBY PRODUCING IN THE LIQUID PHASE OF THE MATERIAL DESCENDING THROUGH THE COLUMN AT A POINT ABOVE THAT AT WHICH VAPORIZATION OF THE WATER AND HYDROCHLORIC ACID TAKES PLACE A RECTIFYING EFFECT BY THE PASSAGE OF THE ACID VAPORS THROUGH SAID DESCENDING MATERIAL, SAID RECTIFYING EFFECT BEING DUE TO THE PARTIAL CONDENSATION OF THE HYDROCHLORIC ACID VAPORS BY THE WATER CONTAINED IN THE COLD MATERIAL ENTERING AT THE TOP OF THE COLUMN AND TO THE FACT THAT THE DESCENDING MATERIAL ALWAYS HAS A LOWER TEMPERATURE THAN THE ASCENDING VAPORS, WHEREBY THE ACID CONCENTRATION IN THE LIQUID PHASE INCREASES RELATIE TO ITS CONCENTRATION AT THE POINT OF INTRODUCTION OF SAID ACID AND REACHES A MAXIMUM AT A POINT NTERMEDIATE THE TOP AND BOTTOM OF THE COLUMN, SAID POINT OF MAXIMUM CONCENTRATION CONSTITUTING A ZONE OF MAXIMUM HYDROLYSIS OFF SAID PENTOSAN CONTAINING MATERIAL, WITHDRAWING THE RESULTANT GASEOUS PRODUCTS CONTAINING FUFURAL AND ACETIC ACID FROM THE TOP OF SAID COLUMN, AND CONTINUOUSLY DISCHARGING THE EXHOUSTED MATERIAL, DRIED AND FREE FROM ACID, FROM THE BOTTOM OF SAID COLUMN. 